Field of the Invention
The invention relates, in general, to pumps and, in particular, to a new and useful dosing pump for liquids, with a piston in a cylinder and suction and pressure phases controlled and moved by a suction valve and a pressure valve and by an oscillating drive mechanism driving through a connecting rod.
In volumetric dosing of liquids, equal volumes of one or more measured secondary liquids must be added in equal time intervals to a primary flow which may comprise either liquid or gaseous substances. The admixture may be either continuous or discontinuous.
In the discontinuous operating mode, the secondary liquid may be bottled in individual, equal volumes, and they must be fed in at equal time intervals. Dosing can be adjusted either by varying the bottle volumina or the time intervals. Piston pumps are the most exact dosing pumps.
One known piston or plunger type of dosing pump is manufactured with piston diameters from 3 to 100 mm so that outputs from a few cm.sup.3 /h up to several m.sup.3 /h are obtained. The volumetric output can be adjusted continuously, usually also even when the pump is running, by varying the piston stroke. This is done by moving the fulcrum of a rocker which transmits the motion coming from the drive motor via an eccentric shaft, already transformed into a reciprocating motion by an eccentric rod, to the piston. The fulcrum shifting device is designed so that the piston always moves to the forward dead center constant for all adjustments. (Hengstenberg-Sturm-Winkler "Measuring and Controlling in Chemical Engineering", Springer 1964, pages 407 to 408). The dosing accuracy depends on the constancy of the piston stroke, and it depends on the inaccuracies of the drive mechanism. The chain of links between the drive motor and the plunger, due to the addition of the play of their bearings which are also subject to wear after a possible adjustment, results in a considerable uncertainty.
Another known piston pump with infinitely variable volume control is the cam pump. Its piston continues outside of the cylinder as a plunger. At its end the plunger supports a roll which follows the cam of a cam shaft. The plunger is spring-loaded in the direction of the cam shaft, i.e. in a suction stroke direction, by a spring resting against a stop. Adjustable nuts on the plunger limit the size of the stroke between the stop and these nuts. Depending on the plunger position, the plunger, through its roll, is in contact with the driven cam during some part of each cam shaft revolution. The pressure stroke occurs under the action of the cam against the spring and the suction stroke under the action of the return force of the spring. Between suction and pressure strokes, the plunger is caught at the stop by the nuts and its guide roll is lifted off the cam (Ullmann's Encyclopedia of Technical Chemistry, Third Edition 1951, Vol. 1 page 98). The accuracy of the volumetric output and its adjustment are limited in that only one end point of the stroke is fixed by the nuts contacting the stop, whereas the other end point is determined by the entire drive mechanism. Even though the spring acts also in the sense of suppressing the bearing play, inaccuracies in operation can nevertheless result, for instance, from the bearings not assuring centricity and, furthermore, from the drive mechanism having to overcome the spring force in addition to the pressure of the medium during the pressure stroke, thus being subject to increased wear. The stop does not engage in the immediate vicinity of the piston, which makes the actually maintained piston end point subject to other environmental influences.